Hemin/G-quadruplex-based Method for Colorimetric Detection of Ochratoxin A in Foods

In order to meet the needs of food safety and realize the rapid,economical and easy detection of Ochratoxin A(OTA)in food was detected based on the colorimetric analysis of hemin/G-quadruplex. Two label-free ssDNA strands were used in which the ssDNA1 was the strand consisted of OTA-aptamer and a G-enriched sequence,and the ssDNA2 was the partial complementary strand of the OTA-aptamer. In the absence of OTA,the two-ssDNA hybridized formed a double-stranded DNA. Hemin exhibited low peroxidase activity due to aggregation because of its low solubility in solution. However,in the presence of OTA,OTA specifically bound with the aptamer and the double stranded DNA was damaged. Hemin bound with the G-enriched sequence formed a hemin/G-quadruplex complex which presented strong peroxidase-like activity and might catalyze the oxidation of hydrogen peroxide and 2,2-diaza-bis(3-ethyl-benzothiazole-6-sulfonic acid)to produce a dark green solution with a maximum absorption at 420 nm. Under the optimized conditions,a linear range of 0.001~2.5 μmol/L(R²＞0.99)of OTA could be achieved,and the detection limit based on 3α/κ(n=10)was 70.3 pmol/L. The as-constructed probe was applied to the detection of OTA in various food samples with the recoveries of 91.9%~109.0%,which indicated that the probe was accurate and sensitive for OTA detection.